This invention relates to a channel translator utilized in a time division digital exchanger and comprising a portion of the speech path equipment. Such channel translator functions to shift digital information of a time division channel of an incoming trunk to the other time division channel of an outgoing trunk.
A time division digital exchanger has a number of features; it can exchange digital signals without decoding the same; its component parts can be miniaturized by using modern LSI technique; and various special functions, for example a conference call circuit, can be incorporated into the exchanger. As a result of improvements in technology, time division electronic exchangers having high efficiency and small size can now be manufactured at low cost.
Generally, the speech path equipment of a time division digital exchanger is constituted by a channel translator comprising a time switch, and a space switch which transfers information between different lines. One example of the construction of the speech path equipment is disclosed in a G. Douglas Johnson's paper "No. 4 ESS-Long Distance Switching for the Future", Bell Laboratories Record, Sep. 1973, vol. 51, No. 8, pages 226-232. The channel translator described in this paper is constituted by substituting electronic hardware for changing the connection by link wires which have been used in a space division type exchanger. For this reason, the digital information sent to the channel translator from such digital transmission line as a PCM 24 channel are sequentially written in a speech data memory device by a writing device in synchronism with the clock pulse of the transmission from the speech data memory device, a first read out device operating in synchronism with the writing device is used to read out the content of a control memory device and a second read out device is operated in response to the read out control information thereby reading out an information of a predetermined address by the control information.
However, since in the prior art channel translator described above, the digital transmission line is connected to the speech data memory device via independent writing and read out devices, the operation lacks flexibility thus decreasing the merit caused by the use of a stored program control system for digital exchanger. Thus, for example, as the capacity of the digital exchanger increases it becomes necessary to change the construction of the channel translator, but where the translator is fabricated with hardware as has been the prior art practice, it is necessary to change the design of the translator each time the capacity is changed. For this reason, it is difficult to expand the capacity and/or add new services.
Furthermore, when special purpose hardware is used as above described, the channel translator becomes relatively bulky whereby the manufacturing cost of a channel translator increases due to a special design. Accordingly, it has been difficult to manufacture an economical exchanger having a small capacity.